Dopamine and glutamate release in the anterior default system during rest: A monkey microdialysis study

Human neuroimaging studies have demonstrated the presence of a default system in the brain, which shows a default mode of brain activity, i.e., greater activity during rest than during an attention-demanding cognitive task. Our previous study on monkeys has revealed a default mode of brain activity in medial cortical areas. We have observed an increase in dopamine (DA) release during a working memory (WM) task compared with that during rest in the monkey lateral prefrontal cortex (LPFC). However, no previous study has examined DA release related to the default mode of brain activity. We used a microdialysis technique to investigate changes in DA release in the medial prefrontal cortex (MPFC), which constitutes the anterior default system, during the WM task and rest. Because DA and glutamate (Glu) release in the LPFC is interrelated, we also examined Glu release in the MPFC. We observed a significant increase in DA release, but no significant change in Glu release during rest compared with that during the WM task. We also observed an inhibitory relationship between the two transmitters in the MPFC. Considering that human default brain activity is related to internal thought processes and increased DA release in the LPFC plays an important role in executive control, increase in DA release during rest in the monkey anterior default system may be related to some form of internal thought process.